Hawaiian tree snails of the subfamily Achatinellinae are unique
to the Hawaiian Islands and highly endangered in the wild. Achatinellines are
arboreal pulmonate gastropods characterized by slow growth and late age at
first reproduction. Objectives of the laboratory studies described here were to
add to the understanding of growth and reproduction of achatinelline snails.
Juvenile Partulina redfieldii (Newcomb) and Achatinella mustelina Migheis were
kept in laboratory environmental chambers with conditions set to emulate
those in the native habitat of P. redfieldii. The snails were provided with fresh
leaves and branches of Metrosideros polymorpha Gaud., a natural substratum
for the snails. Laboratory comparisons of P. redfieldii and A. mustelina maintained
with a natural diet augmented or not with cultures of native fungi grown
on potato dextrose agar revealed that snails of both species grew significantly
faster on the augmented diet and that P. redfieldii attained sexual maturity at
an earlier age. Comparison of growth of P. redfieldii in the laboratory with
similarly sized snails in the field revealed significantly faster growth in the laboratory
animals. There was no significant difference between growth rates of
A. mustelina provided with an augmented food supply in the laboratory and
similarly sized animals in the field. It is likely that food availability limits
growth rate in the field for P. redfieldii, but there is no evidence that growth
in the field for A. mustelina is food-limited. However, the natural diet or
temperature-humidity requirements of A. mustelina may not have been adequately
met in the laboratory, obscuring laboratory-field comparisons. Partulina
redfieldii, collected from the field as adults and maintained in isolation
in the laboratory, produced offspring for at least 4 yr without the opportunity
to outcross. Fecundity of isolated individuals was comparable with
that reported for animals in the field, and there was no indication of fecundity
decreasing over time in isolation. In addition, four of five P. redfieldii isolated
as juveniles attained apparent sexual maturity at ages of 3.2 to ca. 5 yr. A single
offspring was produced by one of these snails, suggesting self-fertilization as
one mechanism allowing the species to reproduce for prolonged periods of time
in the absence of mates.